The development of an effective gonorrhea yaccine is challenged by the antigenic variability of the Neisseria gonorrhoeae (Gc) surface and a lack of information on the correlates of protection against infection. Gc porin is a good vaccine candidate based on its abundance in the outer membrane (OM), limited variability, and its roles in epithelial cell invasion and serum resistance via binding to C4bp-binding protein (C4BP) and factor H (fH). Other promising vaccine targets are MtrE, the OM channel of the MtrCMtrD- MtrE active efflux pump, and OmpA, a conserved OM protein that confers adherence to and invasion of human genital tract cells. Our primary objective is to target surface-exposed loops of GC porin in active and passive immunization strategies against gonorrhea. We will also test the protective efficacy of MtrE and OmpA. Specifically, we will 1) characterize Abs against selected porin loops for in vitro and in vivo correlates of protection and the capacity to block C4BP- and fH-binding to serum resistant strains. The bactericidal and opsonophagocytic activity of Abs against cyclic porin peptides will be measured against Gc strains of different porin types. The capacity of Abs to inhibit porin-mediated invasion of human cervical cells and to block the binding of human fH and C4BP to serum resistant Gc will be tested. We will perform passive protection studies with normal, complement- and granulocyte-deficient mice to identify mechanisms of antibody-mediated protection. We will also ii) develop an active immunization strategy based on cyclic porin loop peptides to protect mice from Gc infection. The optimum dose of peptide and type of adjuvant needed to induce high titer serum and mucosal antibodies with anti-Gc activity will be determined. Mice will be immunized with the most promising peptides, and immunized and unimmunized mice will be challenged intravaginally with the homologous Gc strain to determine if immunization affects susceptibility to infection or colonization load. The local and systemic immune response to two peptides that show protection and an analogous peptide that does not will be thoroughly characterized to define correlates of protection, ill.) Finally, we will investigate the protective potential of MtrE and OmpA as vaccine candidates based on their demonstrated importance in experimental murine infection. We will utilize MtrE- and OmpA-specific antibodies to investigate in vitro correlates of protection and perform immunization/challenge studies with purified MtrE, OmpA and surface-exposed regions of these molecules to measure their potential as vaccine antigens against N. gonorrhoeae in vivo.